The advent of the beadless, i.e., closed torus, tire has dictated the desirability of using wider tires supported on a rear axle assembly which is suspended beneath a vehicle frame by a "soft" suspension system. Such desiderata is difficult to accomplish in respect to conventional suspension systems for off-highway trucks, for example, wherein four tires are normally mounted on a rear axle assembly thereof and require accommodation within a high percentage of available vehicle width. A laterally spaced pair of suspension cylinders, normally utilized in such a suspension system, function to provide both roll and bounce suspension and control.
In addition to giving rise to a spacing problem for accommodating the two cylinders, movement of the cylinders into close proximity to each other will disadvantageously reduce the roll resistance of the rear axle assembly. Furthermore, any attempt to soften the suspension system by reducing the composite spring rate of the cylinders will also function to reduce the desired roll resistance.
One solution to the above problem is to provide a suspension system utlizing a single suspension cylinder, interconnected between the frame of the vehicle and the axle housing proper, in combination with a single suspension device interconnected between the frame and the axle housing and disposed alongside the axle housing. In this type of conventional suspension system a forward end of the axle housing is attached by a universal connection to the frame. Since the latter suspension device is spaced longitudinally between the suspension cylinder and the universal connection, such device is also subjected to relative bouncing as well as rolling movements between the frame and axle housing. Thus, it cannot be made relatively "stiff" and inextensible to solely provide the suspension control during such rolling movements.
Other proposed solutions have included the positioning of a single auxiliary spring suspension device transversely of a ball and socket connection, interconnecting the frame of a vehicle and the rear axle housing thereof. The device is disposed within the confines of the frame and does not provide the desired stability and damping of rolling movements.